Tier 3 — preclinical

Metabolism and pharmacokinetics of 3,3',4',7-tetrahydroxyflavone (fisetin), 5-hydroxyflavone, and 7-hydroxyflavone and antihemolysis effects of fisetin and its serum metabolites

Shia CS, Tsai SY, Kuo SC, Hou YC, Chao PD

Journal of Agricultural and Food Chemistry 2009 57(1):83-9

Bibliography

DOI: 10.1021/jf802378q
PubMed: PMID 19090755
Funding: Not explicitly stated in the reviewed sections; conducted at the Institute of Pharmaceutical Chemistry and School of Pharmacy, China Medical University, Taichung, Taiwan.
Competing interests: Not stated in the reviewed sections.

Study snapshot

Design	Male Sprague-Dawley rats given fisetin, 5-hydroxyflavone, or 7-hydroxyflavone intravenously or orally; serum assayed by HPLC before and after sulfatase/beta-glucuronidase hydrolysis to distinguish parent compound from sulfate/glucuronide conjugates; serum metabolites and fisetin compared for antihemolysis (antioxidant) activity in an AAPH-induced haemolysis assay.
Model	Male Sprague-Dawley rats (pharmacokinetics); rat erythrocytes (in vitro antihemolysis assay).
Sample	Standard rat pharmacokinetic cohort sizes per dosing arm; exact n not stated in the reviewed abstract.
Intervention	Fisetin 10 mg/kg intravenous or 50 mg/kg oral; 5-hydroxyflavone and 7-hydroxyflavone 40 mg/kg oral.
Duration	Standard rat pharmacokinetic sampling timecourse post-dose (serial blood draws via cardiopuncture).
Endpoints	Serum concentration-time profiles of parent flavonoid vs. sulfate/glucuronide conjugates (HPLC, pre/post enzymatic hydrolysis); AAPH-induced erythrocyte haemolysis inhibition (antihemolysis assay) by fisetin vs. its serum metabolites

What the study showed, in plain terms

Fisetin is rapidly broken down in the body, and this study set out to map exactly what it becomes and whether those breakdown products still have antioxidant activity, comparing fisetin with two related but simpler flavones.

Researchers in Taiwan gave rats fisetin (and two comparison flavones) by injection or by mouth, then tracked the parent compound and its conjugated metabolites in blood, and tested how well fisetin versus its serum metabolites protected red blood cells from oxidative damage.

After intravenous dosing, fisetin declined quickly while its sulfate/glucuronide conjugates appeared almost immediately; after oral dosing, unconjugated fisetin was only briefly detectable during absorption before conjugated forms took over. The circulating fisetin metabolites showed weaker antioxidant (antihemolysis) protection than fisetin itself.

Bottom line: reinforces that most fisetin circulating in blood after oral dosing is actually in a conjugated (sulfate/glucuronide) form with reduced antioxidant potency compared with the parent compound, which is relevant context for interpreting oral fisetin bioavailability and dosing claims.

Key findings

After intravenous fisetin (10 mg/kg), parent fisetin declined rapidly while sulfate/glucuronide conjugates appeared almost immediately; after oral dosing (50 mg/kg), unconjugated fisetin was detectable only transiently during absorption, with conjugated forms predominating thereafter. Serum fisetin metabolites showed weaker antihemolysis (antioxidant) activity than fisetin itself. 7-hydroxyflavone was similarly extensively conjugated, while 5-hydroxyflavone was metabolised exclusively to its glucuronide.

What this study can and cannot tell us

Rat pharmacokinetics only; no human PK data. Findings on relative antioxidant potency of metabolites vs. parent compound come from an in vitro haemolysis assay, which may not capture all relevant biological activities of the circulating conjugates in vivo.